Gravity lock for extension ladders

ABSTRACT

A gravity lock for extension ladders, said gravity lock comprising a pair of side struts and a cross-bar which are interconnected to form an A-frame, the lower ends of said side struts being bent inwardly toward each other to form rungengageable hook elements. Where necessary, a flipper is attached to one of said hook elements. By changing the dimensions of the side struts and cross-bar and the angle between them, the gravity lock may be applied in different ways to different kinds and sizes of extension ladders. In one form of the invention, there is a single cross-bar and it is attached to the side struts; in another form of the invention, there are two cross-bars and each is integral with one of the side struts.

Kramer Oct. 30, 1973 GRAVITY LOCK FOR EXTENSION LADDERS PrimaryExaminer-Reinaldo P Machado Att0rneySamuel J. Stoll et al.

[57] ABSTRACT A gravity lock for extension ladders, said gravity lockcomprising a pair of side struts and a cross-bar which areinterconnected to form an A-frame, the lower ends of said side strutsbeing'bent inwardly toward each other to form rung-engageable hookelements. Where necessary. a flipper is attached to one of said hookelements. By changing the dimensions of the side struts and cross-barand the angle between them, the gravity lock may be applied in differentways to different kinds and sizes of extension ladders. In one form ofthe invention, there is a single cross-bar and it is attached to theside struts; in another form of the invention, there are two cross-barsand each is integral with one of the side struts.

4 Claims, 13 Drawing Figures PAIENTEDUBIBO I973 13. 768,594

SHEET 10F 3 GRAVITY LOCK FOR EXTENSION LADDERS BACKGROUND OF THEINVENTION 1. Field of the Invention Extension ladders comprising groundand fly sections and gravity locks which support the fly sections inextended positions on the ground sections.

2. Description of the Prior Art The closest art known to applicant isapplicants own U.S. Pat. No. 3,556,253, issued Jan. 19, 1971. However,the gravity lock disclosed and claimed therein does not have thecapacity for adjustment to the requirements of extension ladders ofdifferent kinds and dimensions.

SUMMARY OF THE INVENTION The present invention provides a gravity lockfor extension ladders, wherein the gravity lock comprises a pair of sidestruts and a cross-bar which interengages the struts to form an A-frame,the lower ends of the struts below the cross-bar being bent inwardlytoward each other to form rung-engageable hooks. A flipper may bepivotally connected to one of said hooks for swingable movement intoengagement with the other of the said hooks.

It will be understood that the gravity lock may be pivotally mounted onthe fly section of the extension ladder for supporting engagement withthe tread portion of the rungs of the ground section of the ladder or,alternatively, it may be pivotally mounted on the ground section of theladder for supporting engagement with the undersides of the rungs of thefly section. In the former case, the A-frame is right-side up; in thelatter case, it is upside down. Also, the cross-bar may be lengthened tospan the width of two rungs (of both the fly and ground sections of theladder) or it may be shortened to engage only a single rung (of eitherthe fly or ground sections of the ladder). By the same token, thecross-bar may be lengthened or shortened, depending upon the width ofthe rungs of.the ladder. The angle between the side struts will beadjusted accordingly.

It will also be understood that the present gravity lock is adjustablein other respects. Thus, either strut (or both struts).may be lengthenedr shortened, depending upon the requirements of individual types andsizes of extension ladders. The cross-bar may be tilted in eitherdirection relativeto the side struts, thereby changing the base anglesaccordingly (the angles be tween the struts and the cross-bar). Thisform of adjustment may be required for mounting the gravity lock on theground section, rather than the fly section (or vice versa) of theladder, and depending on the location of the mounting connectionsrelative to the rungs of the ladder.

The foregoing remarks apply to all forms of the present invention,including the form in which there are two cross-bars and each isintegral with one'of the side struts. In the latter case, the twocross-bars are interconnected to form the effective structural andfunctional equivalent of a single cross-bar. There are substantialadvantages in the design in which the cross-bars are integral with theside struts, for example, in enhanced structural strength, smootherperformance, lessened abrasive effect upon the rungs of the ladder, andsimpler, less costly construction. However, as in the case of all otherforms of the invention, this design (in which the cross-bars and strutsare integrally connected) provides the various adjustment features abovedescribed. Its struts may be lengthened or shortened, its cross-bars maybe lengthened or shortened, and the angles between the struts, andbetween the struts and the cross-bars, may be varied as required by eachindividual application.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view of a ladderembodying a gravity lock made in accordance with one form of theinvention, said gravity lock being shown mounted on the fly section ofan extension ladder, which fly section is slidably disposed on the backof the ground section of the ladder.

FIG. 2 is a longitudinal section therethrough on the line 22 of FIG. 1.

FIG. 3 is an enlarged perspective view of said gravity lock.

FIG. 4 is an enlarged fragmentary transverse section on the line 44 ofFIG. 1.

FIG. 5 is a fragmentary view showing a detail of the gravity lock.

FIG. 6 is a fragmentary longitudinal section showing a gravity lock madein accordance with a second form of this invention, mounted on the flysection ofa differ ent kind of extension ladder wherein the fly sectionis slidably disposed in front of the ground section.

FIG. 7 is an enlarged fragmentary sectional view showing the fly sectionof the ladder being raised and the gravity lock sliding against one ofthe rungs of the ground section of the ladder.

FIG. 8 is a view similar to that of FIG. 7, but showing the fly sectionbeing lowered and showing the flipper of the gravity lock in closedposition to enable the gravity lock to slip past the rungs of the groundsection of the ladder.

FIG. 9 is an enlarged fragmentary section showing the bracket supportfor the gravity lock on the ladder.

FIG. 10 is an enlarged fragmentary section showing the details of theflipper.

FIG. 11 is an enlarged fragmentary transverse section showing a gravitylock made in accordance with a third form of the invention, said gravitylock being mounted on the fly section of a ladder corresponding to theladder shown. in FIG. 6.

FIG. 12 is a vertical section on the line l2-l2 of FIG. 11.

FIG. 13 is an exploded perspective view showing the component parts ofthe gravity lock of FIGS. 11 and 12.

DESCRIPTION OF PREFERRED FORMS OF THE INVENTION FIGQ 1 of the drawingillustrates a representative extension ladder 10 of conventionalaluminum construction, but it will be clearly understood that theinvention is not limited to application to ladders made of aluminum orto the particular ladder design shown in the drawing. It is applicableto all forms of extension ladders, whether made of aluminum, magnesium,wood or any other conventional ladder material.

Extension ladder 10 comprises a ground section 12 (sometimes called basesection), a movable fly section 14 which is slidably mounted on theground section, and a pair of gravity-actuated locks 16 and 18 whichinterengage the two ladder sections to support the fly section inextended position on and relative to the ground section. As isconventional, ground section 12 consists of a pair of left and rightside rails 12a and 12b, respectively, and a plurality of rungs supportedthereby. Similarly, fly section 14 consists of a complementary pair ofleft and right side rails 14a and 14b, respectively, and a plurality ofrungs 22 supported thereby.

Referring now to gravity lock 16, it will be noted that it comprises apair of supporting struts 30 and 32, and a cross-bar 34 whichinterconnects said struts. In this particular design, a flipper 36 ispivotally connected to strut 32.

More specifically, strut 30 comprises a generally straight shank 30a, abent or-curved portion 30b at its lower end, and a widened(press-formed) upper end portion 30c having a hole formed therein toreceive a fastener such as bolt 38. Strut 32 also consists ofa generally straight shank 32a, a bent or curved portion 32b at its lowerend, and a widened (press-formed) upper end portion 320 having a holeformed therein to receive said bolt 38. When a flipper is used, lowerend 32b will have a hole formed therein to receive a second fastenersuch as rivet 40.

Bolt 38 interconnects upper portions 30c and 320 of the two struts andit also pivotally attaches said struts (together with the other elementsof the gravity lock) to rail 14a of fly section 14 of the ladder. Abracket 39 helps secure said bolt to said rail and support it inperpendicular relation thereto. If desired, a bushing or spacer 39a maybe placed on bolt 38 between bracket 39 and rail 14a. It will beobserved that struts 30 and 32 are pivotally supported by bolts 38 (andbushing or spacer 39a, if used) and a washer or spacer 3912 may be usedto enable said struts to clear the adjacent flanges of said rail 14a.

In the preferred form of the invention, struts 30 and 32 are round rodsmade of aluminum or other suitable material, such as steel or iron.Bracket 39 is also made, preferably, of aluminum, but it may be made ofother materials such as steel or iron.

In the preferred form of the invention, cross-bar 34 is a flat aluminumbar (but it may be made of other suitable material such as steel oriron) with a pair of double-ended keyhole-shaped holes 34a and 34bformed therein adjacent its ends to receive struts 30 and 32. It willnow be observed that struts 30 and 32 are pinched above and belowcross-bar 34 to form embossments 30d and 32d thereon.-These embossmentsprevent the struts and cross-bar from shifting relative to each other.Holes 34a and 34b in said cross-bar are shaped like double-endedkeyholes to enable the struts to thread through them despite thepresence of said embossments. After the struts are threaded through saidholes, the' struts are turned 90 and the embossments are thereby movedout of phase or registration with the keyhole extensions of the holes.The struts are now locked to the cross-bar.

It will now be evident that the cross-bar functions as a tie between thestruts,- and when their upper ends are held togetherby .bolts 38, theentire assembly defines an A-frame wherein the struts are its sides andthe cross-bar is its cross-piece. The lower ends 30b and 32b of saidstruts are bent or curved inwardly toward each other to form a pair ofhook-shaped elements adapted to engage rungs 20 and 22 of the twosections of the ladder between them.

Referring now to flipper 36, it will be understood that it may take manyforms and that the form shown in the drawing is merely illustrative.Thus, flipper 36 is made of flat sheet (strip) material folded over todefine a channel section 36a and remaining unfolded at its lower end todefine a generally flat, preferably curved end piece 36b. The upper endof the channel section provides a shoulder 36c which engages the bent orcurved portion 32b of strut 32 and positions the flipper relative to therungs of the ladder.

Thus far, the invention has been described in terms of the extensionladder shown in FIG. 1 of the drawing. In that Figure, the groundsection of the ladder is shown in front of the fly section, that is, thefly section is situated between the ground section and the building orother support against which the ladder rests when in use. In such case,when gravity lock 16 is in locked position to support the fly section inextended position relative to the ground section, cross-bar 34 bearsagainst a pair of rungs 20 and 22 of the two ladder sections (mainlyagainst rung 20). The load of the fly section and of a person standingthereon is thereby supported on rung 20 of the ground section, beingtransmitted thereto through bolt 38 and the gravity lock. Inwardly bentend portions 30b and 32b of the struts function as hooks around rungs 20and 22 and prevent displacement of the gravity lock from said rungs.

In the following description of the operation of the first form of theinvention, a torsion spring 46 around bolt 38 urges the gravity lockforwardly, that is, in the direction away from the wall or othervertical surface against which the ladder is inclined. This spring biasbrings strut 30 of the gravity lock into engagement with rungs 20 of theground section, as will shortly be described.

In the operation of this device, the ladder is placed on the ground orother horizontal support 50 in inclined position against the side wallof a building or other support 52 and pull rope 54 is pulled to raisefly section 14. If necessary, the ladder is tilted slightly away fromthe building to facilitate extension of said fly section. As the flysection rises, struts 30 of the gravity locks will engage successiverungs 20 of the ground section of the ladder, under the bias of springs46, and the gravity locks will thereby be cammed rearwardly (toward wall52) against the spring action. As each rung 20 is passed, the gravitylocks are swung forwardly (away from wall 52) under the action ofsprings 46 and into overlapping or overriding position relative to therung.

When the desired extension has been achieved, that is, when the gravitylocks are elevated above the particular ground section rung 20 on whichthey are to be supported, the fly section is permitted to dropsufficiently to seat cross-bars 34 of the two gravity locks upon'saidrung. The fly section will now be securely supported by the groundsection in extended position.

When it is desired to lower the fly section, it is temporarily raised todisengage the gravity locks from the rung 20 on which they rested. Theladder is then tilted forwardly (toward the vertical) to a slightlysmaller angle of inclination relative to wall 52 and the flippersthereupon swing forwardly to a position wherein they 1 will engage rungs20. The fly section of the ladder is now lowered, and as each rung 20 isengaged by the flippers they are swung upwardly into engagement withcurved end portions 30b of struts 30 of the two gravity locks. Theflippers now function as earns (or cam followers) with respect to saidrung 20, and the two gravity locks are thereby cammed rearwardly toby-pass the said rung and they will then intermittently engage andbypass all successive rungs 20 as the fly section continues its downwardmovement. When the fly section reaches its desired level, the ladder isagain tilted back to its original angle of inclination relative to wall52. This will cause the flippers to swing out of range of rungs 20 andfurther downward movement of-the fly section relative to the groundsection will be blocked by engagement of the gravity locks with the'nextrung 20 to be reached. A

In the second illustrated form of the invention, gravity locks 100 areshown appliedto an extension ladder 102 wherein the fly section 104 isforward of the ground section 106. As shown in the drawing, groundsection 106 supports the ladder on the ground 108 and said groundsection is disposed between the fly section and the vertical wall 1 orother support against which the ladder is inclined.

In this form of the invention there is no need of spring bias toproperly position the gravity locks relative to rungs 112 of the-groundsection. Gravity locks 100 are 'pivotally mounted on side rails 104a ofthe fly section by means of bolts 114 and brackets 116. As is the casewith the gravity lock first above described, gravity locks 100 comprisea pair of struts 100a and 100b, said struts having inwardly bent orcurved lower end portions 100C and 100d, respectively, a cross-bar 100eand a flipper 100f.

It will be noted that the struts and cross-bar define an A-frame ofsomewhat different shape from the A-frame of the gravity lock 16 firstabove described. The reason is that whereas gravity locks 16 are mountedon the rearwardly disposed fly section of extension ladder 10, gravitylocks 100 are mounted on the forwardly disposed fly section of extensionladder 102. In the case of gravity locks 16, a spring is used to urgethem forwardly into engagement with rungs of the forwardly disposedground section. In the case of gravity locks 100, gravity alone swingsthem rearwardly into engagement with rungs 112 of the rearwardlydisposed ground section.

Gravity locks 16 and 100 illustrate the versatility and adaptability ofthe present invention. Its struts may be lengthened or shortened, asrequired by each individual ladder design. So may the cross-bar. By thesame token, the angle between the struts, and between the struts and thecross'ban may be varied to adapt the gravity lock design to the mannerof its application to the ladder (e.g., whether mounted on the forwardor rearward section) and to other factors.

Other variations are encompassed within the scope of the presentinvention. For example, it would be sufficient if the cross-bar wereshortened to engage the rungs of the ground section alone. Also, thegravity locks may be mounted on the ground section, instead of the flysection, of the ladder. In such case, the gravity locks would beinverted so that their cross-bar would engage the underside of theladder rungs (mainly the rungs of the fly section) to support the flysection in elevated position relative to the ground section.

Referring now to the form of the invention wherein there are twocross-bars and they are integral with the side struts (FIGS. 11-13 ofthe drawing), it will be seen that gravity lock 150 comprises a pair ofside struts 152 and 154, a cross-bar 152a which is integral with strut152, an inwardly bent or curved hook element 152b which is integral withcross-bar 152a, a second crossbar 154a which is integral with strut 154and a second hook element 154b which is integral with said secondcross-bar 154a. A flipper 156 may be pivotally connected to hook element154b.

It is evident from the foregoing that, apart from flipper 156, gravitylock consists of only two parts, one comprising strut 152, cross-bar152a and hook 152b, and the other comprising strut 154, cross-bar 154aand hook 154b. However, these two parts define an A- frame ofsubstantially the same configuration as the three-part designspreviously described.

The two parts of the embodiment of the invention now under discussionmay be assembled in any conventional way. One method is to swage theupper end and cross-bar sections of each component so that the combinedthicknesses of these sections will approximate the'unswaged thickness ofeach part. The result will be that, although the two parts are securedin side-by-side relationship at their upper end and cross-bar sections,the over-all thickness of the entire gravity lock assembly will notsubstantially exceed, if at all, the single thickness of the rodmaterial from which the parts are made.

It will be understood from the foregoing that a gravity lock 150 made,for example, of% inch round rod, will be swaged down to 3/16 inchthickness at the upper end and cross-bar sections. Consequently, whenupper end portions152c and 1546 of struts 152 and 154 are swaged,punched, and joined by means of bolt 158, their combined thickness isinch. So, too, when cross-bar portions 152a and 154a are swaged andjoined (by rivets 160 or staples or otherwise), their combined thicknessis also inch.

Gravity lock 150 may be attached to the fly section of an extensionladder, whether the fly section is mounted in front of or behind'theground section, and it may be attached to the ground section, alsoregardless of whether itis disposed in front of or behind the flysection. In short, this is a versatile gravity lock; since it may beadapted to the individual requirements of any kind or size of extensionladder by lengthening or shortening either or both of its struts,lengthening or shortening its cross-bar members, and enlarging ornarrowing the angles which define the triangular top of the A- frame.

I claim:

1. A gravity lock comprising:v

a. a two-piece A-frame consisting of:

b. a first load-bearing strut, cross-bar element and rung-engageablehook,

c. one end of said strut being integral with one end of the cross-barelement, and the rung-engageable hook being integral with the oppositeend of the cross-bar element, and

d. a second'load-bearing strut, cross-bar element and rung-engageablehook,

e. one end of said second strut being integral with one end of thesecond cross-bar element, and the second rung-engageable hook beingintegral with the opposite end of the second cross-bar element,

f. the opposite ends of said first and second struts beinginterconnected to form the sides of the A- frame, and

g. said first and second cross-bar elements being interconnected inside-by-side:relationship to form the cross-piece of the A-frame.

2. A gravity lock in accordance with claim 1,

wherein: I

a. the first mentioned ends of the two load-bearing struts which areintegral with their respective crossbar elements are the lower ends ofsaid struts, and

b. the opposite ends of said load-bearing struts which areinterconnected to form the sides of the A-frame are the upper ends ofsaid struts.

3. A gravity lock in accordance with claim 1,

wherein:

a. a flipper is pivotally connected to one of said rungengageable hooksfor swingable movement into engagement with the other of saidrung-engageable hooks,

b. whereby the space between the two hooks is bridged to prevent entryof a ladder rung,

c. the outer surface of said flipper defining a cam surface which isengageable with the rungs on the other of said ladder sections to camthe A-frame away from them during descent of the fly section relative tothe ground section 4. A gravity lock in accordance with claim 3, whereinthe flipper comprises:

a. a one-piece stamped and formed element;

b. one end of said element being bent longitudinally of the element toform a generally U-shaped configuration in cross-section to wrappartially around the hook to which it is attached;

c. the opposite end of said element comprising a curved tongue adaptedto provide a cam surface engageable with the rungs of said other sectionof the extension ladder.

1. A gravity lock comprising: a. a two-piece A-frame consisting of: b. afirst load-bearing strut, cross-bar element and rungengageable hook, c.one end of said strut being integral with one end of the cross-barelement, and the rung-engageable hook being integral with the oppositeend of the cross-bar element, and d. a second load-bearing strut,cross-bar element and rungengageable hook, e. one end of said secondstrut being integral with one end of the second cross-bar element, andthe second rung-engageable hook being integral with the opposite end ofthe second crossbar element, f. the opposite ends of said first andsecond struts being interconnected to form the sides of the A-frame, andg. said first and second cross-bar elements being interconnected inside-by-side relationship to form the cross-piece of the Aframe.
 2. Agravity lock in accordance with claim 1, wherein: a. the first mentionedends of the two load-bearing struts which are integral with theirrespective cross-bar elements are the lower ends of said struts, and b.the opposite ends of said load-bearing struts which are interconnectedto form the sides of the A-frame are the upper ends of said struts.
 3. Agravity lock in accordance with claim 1, wherein: a. a flipper ispivotally connected to one of said rung-engageable hooks for swingablemovement into engagement with the other of said rung-engageable hooks,b. whereby the space between the two hooks is bridged to prevent entryof a ladder rung, c. the outer surface of said flipper defining a camsurface which is engageable with the rungs on the other of said laddersections to cam the A-frame away from them during descent of the flysection relative to the ground section.
 4. A gravity lock in accordancewith claim 3, wherein the flipper comprises: a. a one-piece stamped andformed element; b. one end of said element being bent longitudinally ofthe element to form a generally U-shaped configuration in cross-sectionto wrap partially around the hook to which it is attached; c. theopposite end of said element comprising a curved tongue adapted toprovide a cam surface engageable with the rungs of said other section ofthe extension ladder.